Add `BadgerDBDeletePipeline` method for `PipelineModel`

[jim-junior]

Description

Extend the PipelineModel struct by implementing a new standalone method called BadgerDBDeletePipeline. To preserve backward compatibility and prevent breaking changes across the orchestration layer, do not change or delete the legacy etcd-based DeletePipeline implementation. This new method will introduce standalone support to remove a stored pipeline record directly from BadgerDB.

Requirements

• File Location: internal/models/pipeline.go
• Method Signature Strategy: Introduce a new method named BadgerDBDeletePipeline(name string) error on the PipelineModel struct.
• Transactionality: Execute both the existence verification and key deletion sequences within a single BadgerDB Update (write) transaction to guarantee state safety.
• Existence Verification & Error Handling: * Prior to running the deletion call, explicitly verify whether the key exists inside BadgerDB.
  • If the key is not found (e.g., catching badger.ErrKeyNotFound), immediately return the descriptive validation error: fmt.Errorf("pipeline not found") to match the exact query parity expected by the model handlers.
• Key Generation: Generate the target storage key using the standard format string: /pipelines/{name}.
• Testing: Create a comprehensive unit test case inside internal/models/pipeline_test.go to validate standalone key deletion, state cleanup verification, and missing item validation handling.

Success Criteria

• The BadgerDBDeletePipeline method is added cleanly alongside legacy methods without breaking public structural boundaries.
• The existence check and key deletion operate atomically inside an exclusive write transaction block.
• Attempting to delete a non-existent pipeline safely drops out with a clear pipeline not found validation error.
• Test Case implementation: A comprehensive unit test is provided that:
  • Seeds an isolated, in-memory BadgerDB database instance with a marshaled JSON mock pipeline configuration.
  • Successfully calls BadgerDBDeletePipeline with the corresponding configuration name.
  • Confirms through a subsequent lookup transaction that the key has been completely deleted from the database.
  • Asserts that invoking the method on an invalid pipeline name accurately triggers the expected "not found" validation response.